The present invention relates to an industrial vehicle and more particularly to an industrial vehicle equipped with a lead-acid battery.
A battery-powered forklift truck equipped with a battery is driven to travel by a traction motor which is driven by electric power from the battery, and a load handling implement mounted on the battery-powered forklift truck is operated by a loading motor to perform load handling operation. In a case that the battery of the battery-powered forklift truck is provided by a lead-acid battery, the amount of electrolyte solution in the battery is decreased by repeated charging and discharging operations of the battery, and the battery is required to be refilled with electrolyte solution. Allowing the battery to be discharged when the volume of electrolyte solution has been already decreased may promote the deterioration of the battery, so that battery life is reduced. There has been proposed an industrial vehicle equipped with a battery which has a electrolyte level sensor for detecting the liquid level of electrolyte solution in the battery, so that the battery is refilled with electrolyte solution when the liquid level detected by the electrolyte level sensor becomes lower than a predetermined level.
Japanese Patent Application Publication No. 7-142099 discloses an electrolyte level warning device for a battery mounted on an electric vehicle. The electrolyte level warning device disclosed in the above Publication No. 7-142099 includes a battery charger, a vehicle battery chargeable by the battery charger, an electrolyte level sensor arranged for the vehicle battery for detecting electrolyte level of the vehicle battery and a light-emitting diode for warning the vehicle operator of any abnormality occurring in the vehicle battery. The battery charger has a microcomputer and a light-emitting diode.
According to the electrolyte level warning device, the electrolyte level detected by the electrolyte level sensor is lower than the predetermined level when charging of vehicle battery by the battery charger is just started, the microcomputer of the battery charger turns on the light-emitting diode for providing a warning to the vehicle operator. This warning prompts a person in charge of battery charging to perform refilling of the vehicle battery with electrolyte solution.
Since the detection of the electrolyte level is performed when the electrolyte level is static during charging of the vehicle battery, the detection can be performed with high accuracy.
Japanese Patent Application Publication No. 2002-120999 discloses a method and a system for controlling battery information of a battery vehicle. In the system for controlling the battery information according to this Publication, an electrolyte level sensor is arranged for a battery of the battery vehicle for monitoring the amount of electrolyte solution in the battery and operable to generate signals on a periodical basis that are indicative of the amount of electrolyte solution to a controller which determines signals and outputs a warning in response to any abnormality of the battery.
However, the electrolyte level warning device disclosed in the above Publication No. 7-142099 is configure just to give a warning when the electrolyte level of the vehicle battery becomes lower than a predetermined level. Meanwhile, in the method and the system for controlling battery information disclosed in the above Publication No. 2002-120999, a warning is given in response to any abnormality of the electrolyte level, but there is no measures proposed to prevent deterioration of the vehicle battery due to discharging while the battery run short of electrolyte solution.
As an example of measures to prevent deterioration of the vehicle battery due to such discharging, the electric vehicle may be stopped immediately when it is found the amount of electrolyte solution becomes insufficient. In such case, however, it is inconvenient to perform refilling of the battery if the refilling station is far from the stopped vehicle. A warning signal, such as light or sound, indicative of shortage of the electrolyte solution may be overlooked by the operator depending on the surrounding environments of the workplace such as warehouse.
The present invention which has been made in light of the above problems is directed to providing an industrial vehicle which prevents deterioration of the battery of the industrial vehicle due to discharging while the electrolyte level of the battery is low and allows the vehicle operator to recognize positively the condition of the battery that its electrolyte level is lowered.